WHINNING

2002 Chevrolet Silverado • 4 cylinder Automatic • 15,000,000 miles

I have a 2002 silverdo pick up truck with over 150,000 that makes a whinning sound, the power steering fluid was running low. It was filled but the sound is still there. I have also noticed my gas hand is becoming unstable. Do u have any idea what this noise whinning could be.